Systematic deletions of the yeast CHS1 and CHS2 genes showed that the nonhomologous amino-terminal portions of the corresponding proteins, chitin synthetases l and 2, are not essential for either enzymatic activity or function. However, small further deletions into the homologous domain, either from the amino or carboxyl terminus, were deleterious to activity and physiological function. A continuing investigation into the architecture of the yeast cell wall led to the isolation of a fraction containing chitin, mannoprotein, beta(1-6) and beta(1- 3)glucan, the structure of which is under study. Preparations of the GTP-binding protein that regulates beta(1- 3)glucan synthetase have been scaled up to isolate sufficient amounts of the protein for further study.